Method and apparatus for reducing NOx emissions

ABSTRACT

In one embodiment, a reductant system comprises: a high pressure reductant pump in operable communication with a power source, wherein the reductant pump comprises a reductant chamber and is capable of pressurizing reductant to a pressure of greater than or equal to 500 psi; a reductant reservoir in fluid communication with the reductant chamber; and an atomizer in fluid communication the reductant chamber. In another embodiment, the reductant system comprises: a reductant pump; system pump in operable communication the reductant pump, a reductant reservoir in fluid communication with the reductant chamber, and an atomizer in fluid communication the reductant chamber. The system pump is configured to provide motive power via a pressurized fluid to the reductant pump, and the system pump is fluidly isolated from a reductant chamber in the reductant pump.

TECHNICAL FIELD

This disclosure relates generally to a method and system for reducing nitrogen oxides (NOx), and more specifically relates to a method and system for reducing NOx emissions from the exhaust gas feedstream.

BACKGROUND

Internal combustion engines emit undesirable pollutants in their exhaust stream. Those pollutants include NOx such as nitrogen monoxide, nitrogen dioxide. NOx is generated from internal combustion engines such as diesel engines, and large combustion apparatuses such as cogenerators. Accordingly, exhaust systems are coupled to the engine to limit and/or remove the pollutants from the exhaust system. Technologies have been and continue to be developed to attenuate these emissions.

NOx is cleaned from exhaust gases of internal combustion engines through the use of catalysts. In addition to removing NOx, these catalysts also remove unburned hydrocarbons (HC) and carbon monoxide (CO). When the engine is operated with a lean air/fuel ratio, the catalyst is efficient at removing the HCs and COs because of the extra oxygen in the exhaust gas. However, the extra oxygen tends to inhibit the removal of NOx. Conversely, when the engine is operated with a rich air/fuel ratio, NOx removal efficiency of the catalyst is increased but the HC and CO removal efficiency is decreased.

In the case of exhaust gas from internal combustion engines operating at stoichiometry (i.e., an air/fuel ratio of nearly balanced stoichiometry for combustion (i.e., about 14.4 and about 14.7) on a mass basis)), NOx is usually removed by using so-called three-way catalysts. (It is noted that stoichiometry (i.e., an air/fuel ratio of nearly balanced stoichiometry for combustion) changes based upon fuel composition, i.e., gasoline, diesel, alcohol, mixtures, etc.) However, in the case of an exhaust gas having a relatively high oxygen concentration, such as those discharged from diesel engines and those discharged from gasoline engines operated lean of stoichiometry, efficient removal of NOx cannot be achieved with the above-described devices. Whereas homogeneous charge engines are able to utilize passive self-contained catalytic reduction techniques as exemplified by the three-way catalyst to control emissions of HC, CO, and NOx, so-called lean-burn engines as exemplified by the compression ignition engine, may have high oxygen content in the exhaust which renders conventional catalysis ineffective. In this case, techniques have been developed to meter an additional chemical reductant or reagent into the exhaust ahead of the reducing catalyst.

Conventional Selective Catalytic Reduction (SCR) of NOx involves injection of aqueous urea solution into the exhaust system ahead of the SCR catalyst. The dosing system is required to accurately meter the solution into the exhaust system, while being responsive to the engine or after treatment control system. Although various techniques of urea introduction to an exhaust system have been tried, many of these techniques require complex equipment and/or controls. What is needed in the art are improved reductant introduction systems.

BRIEF SUMMARY

Disclosed herein are reductant pumps, reductant systems, and methods for using reductant systems. In one embodiment, a reductant system, comprises: a high pressure reductant pump in operable communication with a power source, wherein the reductant pump comprises a reductant chamber and is capable of pressurizing reductant to a pressure of greater than or equal to 500 psi; a reductant reservoir in fluid communication with the reductant chamber; and an atomizer in fluid communication the reductant chamber.

In another embodiment, the reductant system comprises: a reductant pump in operable communication with a power source; system pump in operable communication the reductant pump, a reductant reservoir in fluid communication with the reductant chamber, and an atomizer in fluid communication the reductant chamber. The system pump is configured to provide motive power via a pressurized fluid to the reductant pump, and the system pump is fluidly isolated from a reductant chamber in the reductant pump.

Yet another embodiment of the reductant system comprises: a reductant pump comprising a motor comprising a rotatable shaft, a pump housing with a first pressurizing chamber, a threaded piston keyed into a pump housing, a first end of the threaded piston comprising a first pressurizing surface in fluid communication with a first pressurizing chamber, and a second end of the threaded piston disposed opposite the first end, the second end comprising a second pressurizing surface in fluid communication with a second pressurizing chamber, and a threaded nut in operable communication with threads on the threaded piston. Rotatable shaft rotation rotates the threaded nut producing axial movement of the threaded piston, and axial movement of the threaded piston in a first direction increases pressure of a first fluid in the first pressurizing chamber and creates a vacuum in the second pressurizing chamber, and wherein axial movement of the threaded piston in a second direction increases pressure of a second fluid in the second pressurizing chamber and creates a vacuum in the first pressurizing chamber.

In one embodiment the reductant pump comprises: a motor comprising a rotatable shaft; a pump housing with a first pressurizing chamber; a threaded piston keyed into a pump housing, a first end of the threaded piston comprising a first pressurizing surface in fluid communication with a first pressurizing chamber, and a second end of the threaded piston disposed opposite the first end, the second end comprising a second pressurizing surface in fluid communication with a second pressurizing chamber; and a threaded nut in operable communication with threads on the threaded piston. Rotatable shaft rotation rotates the threaded nut producing axial movement of the threaded piston. Axial movement of the threaded piston in a first direction increases pressure of a first fluid in the first pressurizing chamber and creates a vacuum in the second pressurizing chamber, and axial movement of the threaded piston in a second direction increases pressure of a second fluid in the second pressurizing chamber and creates a vacuum in the first pressurizing chamber.

In one embodiment, the method for providing a reductant to an exhaust system comprises: introducing the reductant to a reductant chamber of a reductant pump; powering the reductant pump with pressurized fluid from a system pump; pressurizing the reductant; and passing the pressurized reductant through an atomizer and into an exhaust flowpath.

The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Refer now to the figures, which are exemplary embodiments and wherein like elements are numbered alike.

FIG. 1 is a schematic view of one embodiment of a NOx removal system.

FIG. 2 is a cross-sectional view of one embodiment of a reductant pump.

FIG. 3 is a schematic view of another embodiment of a NOx removal system.

FIG. 4 is a cut away schematic view of one embodiment of a reductant pump.

FIG. 5 is a schematic view of an in-cylinder embodiment of a NOx removal system.

DETAILED DESCRIPTION

The use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. It is noted that this application is described in relation to use in relation to an exhaust stream. This exhaust stream can be any exhaust stream, e.g., a vehicle exhaust stream (such as an automobile, passenger vehicle, truck, or the like), a cogenerator exhaust stream, or the like.

Disclosed herein is a reductant system, e.g., for injecting reductant (e.g., urea, ammonia, hydrocarbons, or the like) upstream of or into an exhaust treatment device, such as for the removal of NOx from an exhaust stream. Referring now to FIG. 1, a schematic illustration of a system 10 is shown. The system 10 can include an exhaust system of a vehicle as well as parts of other vehicle systems, such as the system pump 52, discussed below. The illustration of FIG. 1 is provided to explain the apparatus and method of exemplary embodiments and should not be considered as limiting. System 10 comprises an exhaust path 12 having an inlet opening 14 and an outlet opening 16. Inlet opening 14 is in fluid communication with an exhaust of an engine (not shown) and the outlet 16 opening is in fluid communication with ambient atmosphere.

Disposed within exhaust path 12 is an exhaust treatment device 20. The exhaust treatment device 20 may include such treatment devices as, but not limited to: an SCR catalyst, a NOx catalyst, a NOx adsorber, or the like. A reductant pump 24 is positioned to provide a pressurized flow of reductant to an outlet conduit 26, having an atomizer 28 disposed on one end, in the exhaust path 12. The reductant may be any material capable of reducing the NOx, such as ammonia, urea, and the like. As used herein the term “urea” is meant to encompass urea in all of its commercial forms, including those containing: ammelide; ammeline; ammonium carbonate; ammonium bicarbonate; ammonium carbamate; ammonium cyanate; ammonium salts of inorganic acids, including sulfuric acid and phosphoric acid; ammonium salts of organic acids, including formic and acetic acid; biuret; cyanuric acid; isocyanic acid; melamine and tricyanourea. Atomizer 28 is positioned to provide an atomized spray of reductant in the exhaust as it flows towards the exhaust treatment device 20. The spray of reductant in combination with the exhaust treatment device 20 reduces unwanted exhaust emissions. Reductant pump 24 is in fluid communication with a reservoir 30 of reductant 32 via a conduit 34. In the disclosed embodiments, the reductant is injected into the exhaust path without the need of a carrying medium, such as compressed air.

An optional heater 46, with is in thermal communication with the reductant and is for heating the reductant 32, may be provided to prevent reductant 32 from freezing when exposed to temperatures below the freezing point of the reductant 32. Additionally or in the alternative, an optional expansion bladder 48 may be located within the reservoir 30. The expansion bladder will allow the reductant to freeze and expand, without damaging the reservoir.

In one embodiment, the flow path of the reductant 32 through the system 10 comprises reductant 32 exiting the reservoir 30 through conduit 34, through a purge solenoid 50, to the reductant pump 24. The reductant pump 24 may be powered by a pressurized fluid provided by a system pump 52, e.g., a fluid that is already present in the system in which the reductant system is employed (e.g., a vehicle system pump, such as power steering fluid, and the like), and the like. A control valve 53 directs the pressurized fluid from the system pump 52 to the reductant pump 24. The system pump 52 may be, but is not limited to one of the following devices: power steering pump, fuel pump and air compressor. The pressurized fluid therefore may be power steering fluid, fuel, and air, respectively.

The outlet of the reductant pump 24 is in fluid communication with a purge bypass valve 54 and a solenoid valve 56. The solenoid valve 56 is controlled by an engine control unit 36 or a separate reductant control unit. Based upon signals received by the engine control unit 36, it activates the solenoid valve 56 and allows the reductant 32 to travel through the atomizer 28 into the exhaust path 12 ahead of the exhaust treatment device 20.

Accordingly, the engine control unit 36 can provide the necessary commands to the various components in the exhaust system to limit NOx emissions. The engine control unit 36 may comprise a microprocessor and associated control algorithm(s). This unit may be in operable communication with various components of the system 10, such as sensors capable of providing signals indicative of operating parameters. These signals, when applied to the control algorithm(s) cause an appropriate operating signal to be sent to the system components.

Although, up to now, an exhaust path reductant introduction has been discussed, it should be clear that the disclosed method and apparatus may be adapted for use in an in-cylinder reductant introduction. Therefore, depending on the type of reductant introduction (e.g., exhaust path or in-cylinder), the plurality of sensors may comprise, but are not limited to, reductant flow temperature sensor(s) 38 (e.g., thermocouple(s)), reductant flow pressure sensor(s) 39, inlet NOx sensor(s) 40, catalyst temperature sensor(s) 41, outlet NOx sensor(s) 42, ammonia sensor(s) 44, reductant level sensor(s) (not shown), reductant tank temperature sensor(s) 43, cylinder pressure sensor(s) (not shown), air mass flow sensor(s) (not shown), humidity sensor(s) (not shown), engine speed sensor(s) (not shown), fuel delivery sensor(s) (not shown), boost pressure sensor(s) (not shown), boost temperature sensor(s) (not shown), cylinder pressure sensor(s), exhaust treatment device temperature sensor(s) (e.g., in thermal communication with the exhaust treatment device), and the like, as well as combinations comprising at least one of the foregoing. Accordingly and through the use of the plurality of sensors, real-time and/or non-real-time post-catalyst monitoring of NOx emissions for NOx reduction confirmation are available.

The engine control unit 36 processes signal(s) selected from the above sensors according to a method for carrying out a control algorithm. The engine control unit 36 makes changes to engine operating conditions according to the method in order to reduce NOx emissions.

The method for carrying out a control algorithm for reducing NOx emissions described above can be embodied in the form of computer-implemented processes and apparatuses for practicing the method. The method can also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer and/or controller, the computer becomes an apparatus for practicing the method. Existing systems having reprogrammable storage (e.g., flash memory) can be updated to implement the described method.

The embodiment shown in FIG. 1 may have an optional reductant purge system comprising the purge bypass valve 54 and purge solenoid 50. During certain operating conditions, temperatures may get cold enough such that any reductant remaining in the lines of the system 10 may freeze. The purge system will purge the reductant from the lines in the system 10 by directing air from the vent 58 to the pump 24. The pump 24 compresses the air, which is then used to purge reductant from the system lines. The bypass purge valve 54 may be activated to direct pressurized air through an activated purge solenoid 50 and back into the reservoir 30, thereby purging the line between the reductant pump 24 and the reservoir 30 of reductant. Similarly the bypass purge valve 54 may be activated to direct pressurized air through the activated solenoid valve 56 and out into the exhaust path 12, thereby purging the line between the reductant pump 24 and the atomizer 28. Any small amount of purged reductant left in the exhaust path should not cause any damage upon freezing. Therefore, the atomizer 28 is fluidly isolated from a carrier gas (e.g., air from the environment, air, or the like) during reductant injection (e.g., no carrier gas is needed to introduce reductant to the exhaust path 12), and may be in fluid communication with a gas (e.g., air) purge during purging. For example, the atomizer preferably has a single input to receive high pressure reductant (e.g., reductant having a pressure of greater than or equal about 500 pounds per square inch (psi)).

FIG. 2 provides a cross-sectional schematic view of an embodiment of the reductant pump 24. The pump 24 comprises a pressurizing chamber 62, a de-pressurizing chamber 64, and a reductant chamber 66. The pressurizing chamber 62 has a first port 67 in fluid communication with the control valve 53 (see FIG. 1), the depressurizing chamber 64 has a second port 69, also in fluid communication with the control valve 53. The reductant chamber 66 has a reductant inlet port 70 in fluid communication with conduit 34, and a reductant outlet port 72, in fluid communication with conduit 26.

A piston 74 may be actuated by pressurized fluid from the vehicle system pump 52, whereby the piston 74 will pressurize the reductant. The piston 74 has three force transmitting surfaces: a pressurizing surface 76, a de-pressurizing surface 78 and a reductant pressurizing surface 80. The pressurizing surface 76 is much larger than the reductant pressurizing surface 80, thus giving the pressurizing surface 76 a mechanical advantage over reductant pressurizing surface 80. The piston 74 is shown at or near the top of its stroke in FIG. 2. At this point reductant is fed into the reductant chamber 66 via the reductant inlet port 70. Once the reductant chamber 66 receives the reductant, pressurized liquid is directed by the control valve 53 (see FIG. 1) through the first port 67 into the pressurizing chamber 62. Simultaneously, the control valve 53 also directs the pressurized liquid from the de-pressurizing chamber 64 to a liquid tank (e.g. the system pump 52) so that the de-pressurizing chamber 64 can release its pressure from the previous cycle (if there was a previous cycle). The pressurized liquid pushes against the pressurizing surface 76 thereby moving the piston 74 down and causing the pressurizing of the reductant in the reductant chamber 66. Reductant inlet port 70 has a check valve, thereby permitting the pressurizing of the reductant without reductant escaping through port 70. At or near the bottom of the piston's stroke the reductant outlet port's check valve is opened, and the pressurized reductant exits the chamber 66 via the reductant outlet port 72. At this point, the control valve 53 directs pressurized liquid into de-pressurizing chamber 64 via second port 69, simultaneously; the control valve 53 also directs the pressurized liquid from the pressurizing chamber 62 to a liquid tank, which may be associated with the system pump 52 so that the pressurizing chamber 62 can release its pressure. The pressurized liquid pushes up against the de-pressurizing surface 78, thereby moving the piston up which in turn causes a vacuum to draw reductant into the reductant chamber 66 via inlet port 70 (with the inlet port's check valve open and the outlet port's check valve closed). Once reductant has entered the chamber 66, the cycle starts again.

Because reductant chamber 66 is separated from pressurizing chamber 62 and de-pressurizing chamber 64, there is little to no chance of pressurizing fluid leaking into the reductant, or reductant leaking into the pressurizing fluid. If reductant bypasses O-rings 79, the reductant will merely enter the space 83, which can be open to the atmosphere (as illustrated), and will not contaminate the fluid from the vehicle system pump 52. Similarly, if pressurized fluid leaks past O-rings 81, the fluid will not contaminate the reductant, but will merely enter the space 83.

The reductant pump 24 should be configured to provide enough reductant to the exhaust path to reduce the NOx emissions. For example, the reductant pump 24 may have a bore diameter of about 0.25 to about 2 inches (about 0.64 to about 5.1 centimeters), a stroke of about 0.25 to about 2 inches (about 0.64 to about 5.1 centimeters), and a reductant chamber size of approximately about 0.1 to about 2 cubic inches (about 1.6 to about 32.8 cubic centimeters). Of course the disclosed reductant pump may be configured into a variety of different sizes. The size of the reductant pump is dependent on many factors, such as engine size, type, use, and the like.

FIG. 3 shows another embodiment of a system. In this embodiment, an electric pump 82 is in fluid communication with the reservoir 30 of reductant 32 via the conduit 34. The electric pump 82 is in fluid communication with an accumulator 84. The accumulator is in fluid communication with the atomizer 28 via the solenoid valve 56. The accumulator 84 dampens pressure fluctuations in the reductant and allows the electric pump 82 to operate intermittently rather than running at all times when reductant is being injected into the exhaust path. The electric pump 82 may be in operable communication with the engine control unit 36 and/or in operable communication with a pressure sensor 39.

In another embodiment, the electric pump 82 will only activate when the pressure sensor 39 indicates a reductant pressure below some set point, thus preventing an energy consuming continuous operation of the electric pump 82. The arrows indicate the flow direction of the reductant from the conduit 34 though the electric pump 82 and the accumulator 84 to the solenoid valve 56.

FIG. 4 shows an embodiment of the electric pump 82. An electric motor 86 turns a shaft 88. The shaft 88 may have a worm thread 90 on its outer surface. As the shaft 88 and worm thread 90 rotate, the worm thread turns a worm gear 91. The worm gear 91 is in operable communication with a first bevel gear 92, which turns a second bevel gear 94. A threaded nut 96 is in operable communication with the second bevel gear 94, and turns with the bevel gear 94. As the nut 96 turns, it moves a threaded piston 98 in an axial direction represented by the arrow. The embodiment shown may be configured such that when the motor shaft 88 turns clockwise the threaded piston 98 moves to the left, and when the motor shaft 88 turns counter-clockwise the threaded piston moves to the right. Of course the electric pump may be configured such that when the motor shaft 88 turns clockwise the threaded piston 98 moves to the right, and when the motor shaft 88 turns counter-clockwise the threaded piston 98 moves to the left.

The piston 98 is shown at the end of its left stroke. At this point, the pressurized reductant in the first reductant chamber 100 flows out of a first port (outlet) 102 and into the optional accumulator 84. As the motor reverses direction and the piston rod begins to move to the right, thus compressing reductant in the second reductant chamber 104, reductant is drawn from the tank by vacuum caused by the displacement of the piston into the first reductant chamber 100 via the second port (inlet) 106. The third port (inlet) 108 and fourth port (outlet) 110 each have check valves 112 and 114, of which 114 is closed during this point in the piston stroke, thus preventing the reductant from returning to the tank and escaping the second chamber 104. Similarly second port (inlet) 106 has a check valve 116 that is open, and first port (outlet) 102 has a check valve 118 that is closed. Once the piston rod has moved to the right to develop sufficient pressure in chamber 104, check valve 114 opens and the reductant exits the chamber 104 via fourth port 110 to the accumulator 84. At the end of the right stroke, the motor reverses direction again, and the piston 98 begins moving to the left whereupon check valve 112 opens, allowing reductant to flow from the reservoir (e.g., tank) 30 into chamber 104, and check valve 116 closes thus preventing the reductant in chamber 100 from escaping as it is being pressurized. This embodiment of an electric pump using a worm gear advantageously provides a high torque with small power requirements.

The electric reductant pump 82 can be configured such that it can provide sufficient reductant to the exhaust path to reduce NOx emissions. Thus, in an exemplary embodiment, the bore of the electric reductant pump 82 may be about 0.13 to about 2 inches (about 0.33 to about 5 centimeters), a stroke of about 1 to about 8 inches (about 2.5 to about 20.3 centimeters), and a reductant chamber size of about 0.1 to about 2 cubic inches (about 1.6 to about 32.8 cubic centimeters).

In addition to the in-exhaust injection of reductant as discussed above with regard to FIGS. 1-4, it is possible to inject reductant into the cylinders of the engine, as for example in commonly owned and assigned U.S. Pat. No. 6,679,200 B2, filed Jun. 27, 2002, and issued Jan. 20, 2004. An example of such an application is illustrated in FIG. 5 wherein a reductant pump 124 is positioned to provide reductant into a cylinder 120 of an engine 122. Of course, the number of pumps may vary with the number of cylinders requiring reductant. Since the timing of this injection occurs late during the engine expansion stroke, the pump 124 provides an injection pressure high enough to overcome the cylinder pressure. Other known reductant injection systems have only low-pressure capability, and thus far, are unsuitable for in cylinder applications.

The reductant pumps described herein may be used in conjunction with many different types of atomizers. These include the simple open orifice nozzle, an inward opening closed nozzle, an outward opening top poppet nozzle (e.g., U.S. Pat. No. 4,116,591), a vaporizing nozzle, and many others. The atomizer may be located centrally and axially within the exhaust pipe section, or may be located externally on the exhaust periphery and projecting across the pipe or duct. In all cases, the objective is to select an atomizer appropriate to be the specific system geometry, which will achieve the complete homogeneous mixing of reductant and exhaust gas, and preferably in the shortest possible length. The reductant injection system described here has a wider potential selection of atomizer technologies and geometries that than is available to air-assisted designs. Thus, it can be expected to offer greater application flexibility.

In an exemplary embodiment, the amount of reductant injected into the exhaust stream would be about 1 part volume of reductant to every 20 parts volume of fuel. Of course this amount of reductant is dependent on various factors, including, but not limited to: the size and type of the engine, types of uses for the engine, and atmospheric conditions. Therefore a possible reductant volume may be about 1 part reductant for every 100 parts of fuel to 1 part of reductant for every 5 parts of fuel.

Systems without a high pressure pump generally introduce reductant (at a pressure of 35 psi to 50 psi) to an injector. Air, at a pressure of 50 psi to 100 psi is also introduced to the injector. The air breaks up the reductant to small particles that are introduced to the exhaust stream. Such a system uses a dedicated air compressor that is not always available.

In contrast, the disclosed reductant system employs a high pressure pump that pressurizes the reductant to a pressure sufficient to atomize the reductant to a desired particle size without the use of a carrier gas. For example, the high pressure pump pressurizes the reductant to a pressure of greater than or equal to about 500 psi, with a pressure of greater than or equal to about 700 psi preferred, and a pressure of greater than or equal to about 900 psi even more preferred. The pressurized fluid, which may be stored in an accumulator, is introduced to an atomizer and injected into an exhaust stream. Since the atomizer receives a high pressure reductant, it can efficiently atomize the reductant without a carrier gas. Hence the atomizer can have a single inlet.

In the disclosed embodiments, the system may advantageously provide atomized reductant into the exhaust path (e.g., upstream of an exhaust treatment device and/or into an exhaust treatment device) without the need for a separate air supply and air compressor. The disclosed embodiments are lighter and less expensive than the currently used reductant injection systems, because heavy air compressors and heavy air lines able to withstand the pressures of the compressed air are not necessary. Further, in some of the disclosed embodiments, the system may use pressurized fluids from other systems in the automobile, such as power steering fluid, brake fluid, and others. The disclosed embodiments may also be employed for direct injection of reductant into the combustion cylinders.

While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A reductant system, comprising: a reductant pump in operable communication with a power source, wherein the reductant pump comprises a reductant chamber and is capable of pressurizing reductant to a pressure of greater than or equal to 500 psi; a reductant reservoir in fluid communication with the reductant chamber; and an atomizer in fluid communication the reductant chamber.
 2. The reductant system of claim 1, wherein the power source is a system pump, wherein the system pump can provide motive power via a pressurized fluid to the reductant pump, and wherein the system pump is fluidly isolated from the reductant chamber.
 3. The reductant system of claim 1, wherein the reductant reservoir is in thermal communication with a reductant heater.
 4. The reductant system of claim 1, wherein the reductant reservoir comprises an expansion bladder.
 5. The reductant system of claim 1, further comprising: a vent in fluid communication with the reductant reservoir and the reductant chamber; and a purge bypass valve in fluid communication with the atomizer and the reductant reservoir for directing fluid from the reductant chamber to at least one of the atomizer and the reductant reservoir.
 6. The reductant system of claim 1, further comprising a control unit capable of varying an output of the reductant pump in response to a signal from a temperature sensor in thermal communication with an exhaust treatment device.
 7. The reductant system of claim 1, further comprising: a first NOx sensor located upstream of the exhaust treatment device; a second NOx sensor located downstream of the exhaust treatment device; and an ammonia sensor located downstream of the exhaust treatment device.
 8. The reductant system of claim 1, wherein the reductant pump further comprises: a piston, the piston comprising a first actuating surface, a second actuating surface, and a reductant pressurizing surface; wherein the reductant chamber is in fluid communication with an inlet check valve and an outlet check valve, and is in fluid communication with the reductant pressurizing surface; a first actuating chamber in fluid communication with the first actuating surface and in fluid communication with a first port; and a second actuating chamber in fluid communication with the second actuating surface and in fluid communication with a second port; wherein movement of the piston in a direction will increase the pressure of fluid received in the reductant chamber.
 9. The reductant system of claim 8, further comprising a spacer chamber disposed between the second actuating chamber and the reductant chamber such that a fluid leaking from the second actuating chamber will escape from the reductant pump and will not enter the reductant chamber, and reductant leaking from the reductant chamber will escape from the reductant pump and will not enter the second actuating chamber.
 10. A reductant system, comprising: a reductant pump; system pump in operable communication the reductant pump, wherein the system pump is configured to provide motive power via a pressurized fluid to the reductant pump, and wherein the system pump is fluidly isolated from a reductant chamber in the reductant pump; a reductant reservoir in fluid communication with the reductant chamber; and an atomizer in fluid communication the reductant chamber.
 11. A method for providing a reductant to an exhaust system, comprising: introducing the reductant to a reductant chamber of a reductant pump; powering the reductant pump with pressurized fluid from a system pump; pressurizing the reductant to a pressure of greater than or equal to about 500 psi; and passing the pressurized reductant through an atomizer and into an exhaust flowpath.
 12. The method of claim 11, further comprising introducing the reductant upstream of an exhaust treatment device.
 13. The method of claim 11, wherein the pressurized reductant is injected without a carrier fluid.
 14. The method of claim 11, further comprising purging a reductant system by introducing a purge fluid to the reductant chamber; powering the reductant pump with the pressurized fluid from a system pump; pressurizing the purge fluid; purging a flow path between the reductant pump and the atomizer with the pressurized purge fluid; and purging a flow path between the reductant pump and a reductant reservoir with the pressurized purge fluid.
 15. The method of claim 14, comprising purging the reductant system of reductant when an ambient temperature is below a setpoint.
 16. The method of claim 14, further comprising pumping the pressurized reductant into an accumulator prior to injecting it into the exhaust flow path.
 17. A reductant system, comprising: a reductant pump comprising a motor comprising a rotatable shaft; a threaded piston keyed into a pump housing, a first end of the threaded piston comprising a first pressurizing surface in fluid communication with a first pressurizing chamber, and a second end of the threaded piston disposed opposite the first end, the second end comprising a second pressurizing surface in fluid communication with a second pressurizing chamber; and a threaded nut in operable communication with threads on the threaded piston; wherein rotatable shaft rotation rotates the threaded nut producing axial movement of the threaded piston; and wherein axial movement of the threaded piston in a first direction increases pressure of a first fluid in the first pressurizing chamber and creates a vacuum in the second pressurizing chamber, and wherein axial movement of the threaded piston in a second direction increases pressure of a second fluid in the second pressurizing chamber and creates a vacuum in the first pressurizing chamber.
 18. The reductant system of claim 17, further comprising: a reductant reservoir in fluid communication with the first pressurizing chamber and the second pressurizing chamber; an accumulator in fluid communication with the first pressurizing chamber and the second pressurizing chamber; and an atomizer in fluid communication the accumulator.
 19. The reductant system of claim 17, further comprising a reductant heater in thermal communication with the reductant reservoir.
 20. The reductant system of claim 17, wherein the reductant reservoir comprises an expansion bladder.
 21. The reductant system of claim 17, wherein the reductant pump further comprises: a worm gear disposed on an outer surface of the rotatable shaft; a first bevel gear in operable communication with the worm gear; and a second bevel gear in operable communication with the first bevel gear, and annularly affixed to an outer surface of the threaded nut. 